The invention relates to a water tight seal structure for camera, which may be used with an externally exposed control of a camera such as a winding lever, shutter button, film rewind shaft, for example.
A precision instrument such as camera or watch has its externally exposed parts provided with a water tight seal structure to protect them against rain, splashes of water, inadvertent drop into the water or to permit a positive use in water. A water tight seal structure for these exposed parts, in particular, one associated with a movable part which is used to provide a control must be constructed to achieve the sealing function without detracting from the operating ease of the control, which is difficult to achieve.
FIG. 1 illustrates an exemplary water tight seal structure used in the prior art with a movable part of a camera which is shown in cross section. It is to be understood that the illustration is limited to the lefthand part of the instrument. In FIG. 1, frame 1 represents a cover which encloses the entire assembly such as a camera. Frame 1 is formed with opening 5 to receive rotating shank body 4 which may constitute a shutter button, a winding lever, a film rewind shaft or a like movable member. Intermediate its length, the wall of opening 5 is formed with peripheral groove 2 therein in which O-ring 3 is disposed which is formed of rubber and elliptical in cross section. The outer, the upper and the lower surface of O-ring 3 tightly engages the bottom, the upper and the lower surface of peripheral groove 2 while the inner surface of O-ring 3 tightly engages an outer peripheral surface of rotating shank 4. Shank body 4 includes shank 4a which is disposed within opening 5, and disc 4b which is formed integrally with the upper end of shank 4a and projecting outside opening 5 and which is connected with an external rotatable control. The bottom end of shank 4a is formed as threaded portion 4c of a reduced diameter which is threadably engaged by lock nut 6.
In the seal structure described above, the tight engagement between O-ring with peripheral groove 2 on one hand and the outer peripheral surface of shank body 4 is intended to prevent an ingress of pressurized water into the interior of the instrument through a gap between frame 1 and shank body 4 as indicated by arrow A.sub.0. However, the reduced area of contact between O-ring 3, shank body 4 and peripheral groove 2 is insufficient to provide a satisfactory water sealing function, allowing pressurized water to find its way into the interior through a clearance between O-ring 3 and shank body 4 and a clearance between O-ring 3 and peripheral groove 2, as indicated by arrows A.sub.1, A.sub.2.
In addition, since shank body 4 is supported by frame 1 only by the inner peripheral surface of O-ring 3 in addition to the support by nut 6, a clearance is likely to occur as shown between the inner peripheral surface of frame 1 and the outer peripheral surface of shank body 4, giving rise to a rattling of shank body 4. Furthermore, the spacing between frame 1 and shank body 4 is subject to variation, resulting in a varying momentum required to rotate shank body 4, making its operation more difficult.